Oxidative Catalytic Fractionation of Lignocellulose Enhanced by Copper–Manganese-Doped CeO2

Abstract

Oxidative catalytic fractionation (OCF) represents an efficient approach to valorize lignocellulose for coproduction of monophenols and cellulose. To achieve an adequate monophenol yield, lignin oxidation, typically, requires high O₂ pressure and an excess of Cu catalysts (the Cu dosage is approximately 3–5 mol equiv relative to the aromatic units in lignin). However, these conditions are relatively harsh for cellulose, resulting in severe decomposition to aliphatic acids. To address the trade-off between the monophenol yield and cellulose production, we develop an enhanced OCF using a CuMnCeO₂ solid solution as the catalyst. Under relatively mild conditions (specifically, 0.1 MPa O₂), 28.7 wt % monophenols were released from birch, using catalytic amounts of Cu (the Cu dosage was about 0.03 mol equiv relative to the aromatic units in lignin). Meanwhile, up to 83.9% of cellulose was collected as a solid pulp. The synergistic effect between doped metals (Cu and Mn) and oxygen vacancies was found to be crucial for enhanced lignin oxidation under mild conditions with minimized cellulose loss. The abundant surface oxygen vacancies facilitated oxygen activation by well-dispersed Cu and Mn species, while the strong interaction between these metals enhanced the catalyst’s reducibility. Key intermediates such as β-vinyl aryl ethers and byproduct glycolic acid were identified by model experiments, confirming that lignin oxidation primarily followed a 1,2-dioxetane homolysis mechanism. Overall, this enhanced OCF demonstrates the potential viability of lignin oxidation in practical biorefinery applications.